The common phosphate minerals, apatite Ca5(PO4)3(F,OH,Cl), monazite (Ce,La,Th)PO4, and xenotime YPO4, have found widespread use in geochronology because they incorporate U and Th into their structures. For example, apatite usually has a few tens of ppm of both U and Th, while monazite and xenotime usually have hundreds of ppm to weight percent levels of these elements. As a consequence, these phosphates can be dated using several fundamentally different isotopic techniques. Elsewhere in this volume Harrison et al. describe phosphate dating using ingrowth of radiogenic Pb, the final daughter of...